The present invention relates to antivibration sleeves and to motor vehicles including such sleeves.
More particularly, the invention relates to an antivibration sleeve comprising:
a rigid inner strength member which extends longitudinally along a central axis; and
at least a first rigid annular strength member which surrounds the inner strength member and the central axis, and at least one elastomer body connecting the inner strength member to the first annular strength member, said elastomer body including two diametrically opposite arms each extending along a first radial direction from the inner strength member to said first annular strength member, the elastomer body being shaped so that the antivibration sleeve presents relatively high elastic stiffness in said first radial direction and lower elastic stiffness in a second radial direction substantially perpendicular to said first radial direction.
Document DE-A-34 41 560 describes an example of such an antivibration sleeve for connecting a vehicle rear axle to the vehicle body. In that document, the central axis of the antivibration sleeve is disposed vertically, which provides numerous advantages, in particular:
it is possible to select the elastic stiffness of the antivibration sleeve along its central axis independently of its stiffness along the first and second radial directions, thereby making it possible in particular to obtain an antivibration sleeve that presents low stiffness along its central axis, thus improving the comfort of the vehicle; and
it is possible to select optimum orientations for the first and second radial directions relative to the longitudinal direction of the vehicle, when designing the rear axle.
Nevertheless, that type of assembly presents the drawback that when the sleeve is to carry static vertical forces, e.g. due to the weight of the vehicle and the rear suspension, the arm of the elastomer body is subjected to shear stresses, and possibly even to traction stresses, and that is harmful to the longevity of the elastic body.
A particular object of the present invention is to mitigate that drawback.
To this end, according to the invention, in an antivibration sleeve of the kind in question:
the inner strength member presents, at least in register with the two arms of the elastomer body, two wedge-shaped bearing zones which extend so as to converge towards the central axis in a first direction parallel to said central axis;
the first annular strength member also presents, at least in register with the two bearing zones of the inner strength member, first and second complementary bearing zones in the form of wedges which converge towards the central axis in said first direction; and
each arm of the elastomer body is bonded to at least one of the bearing zones of the inner strength member and to one of the complementary bearing zones of the first annular strength member.
By means of these dispositions, the antivibration sleeve of the invention is adapted to supporting a static axial load urging the inner strength member in the first direction relative to the first annular strength member and to do so without any harmful effect on the lifetime of the antivibration sleeve.
Because of the wedge-shaped bearing zones provided on the inner strength member and on the first annular strength member, the axial static load supported by the antivibration sleeve becomes a compression prestress in the elastomer body. Such compression prestress is well accepted by the elastomer body and gives rise to no accelerated aging of the antivibration sleeve; on the contrary, said compression prestress prevents or limits the appearance of traction stresses when the inner strength member is subjected to vibratory motion relative to the first annular strength member (i.e. while the vehicle is running and the antivibration sleeve of the invention is used to connect a vehicle rear axle to the vehicle body).
In preferred embodiments of the invention, it is possible also to make use of one or more of the following dispositions:
the elastomer body is overmolded on the first annular strength member and said first annular strength member is surrounded by a second strength member which is secured to the first annular strength member and to the elastomer body, co-operating with said elastomer body to define first and second hydraulic chambers filled with liquid and separated from each other by the two arms of the elastomer body, the first and second hydraulic chambers communicating with each other via at least one narrow passage which is provided between the first bearing zone of the first annular strength member, and the second strength member;
the first bearing zone of the first annular strength member co-operates with the second annular strength member to define a first liquid duct which extends in a circumferential direction about the central axis and which communicates firstly with the first hydraulic chamber and secondly with the second hydraulic chamber, said first liquid duct presenting a flow section that is at least three times greater than the flow section of said narrow passage, the elastomer body having a first axial rib which extends radially and parallel to the central axis from the first bearing zone of the first annular strength member to an outside edge in contact with the second annular strength member, said first axial rib thus closing the first liquid duct and presenting sufficient flexibility to enable a certain amount of decoupling between the inner strength member and the first and second annular strength members with respect to at least some radial vibrations at a frequency lying in the range 5 hertz (Hz) to 50 Hz;
the elastomer body further includes a bead which extends in the circumferential direction between the first bearing zone of the first annular strength member and the second annular strength member, said bead cooperating with the second annular strength member to define said narrow passage and also defining part of the first liquid duct;
the second bearing zone of the first annular strength member co-operates with the second annular strength member to define a second circumferential liquid duct which communicates firstly with the first hydraulic chamber and secondly with the second hydraulic chamber, and the elastomer body includes a second axial rib which extends radially and parallel to the central axis from the second bearing zone of the first annular strength member to an outside edge in contact with the second annular strength member, the second axial rib closing the second liquid duct and presenting sufficient flexibility to enable a certain amount of decoupling between the inner strength member and the first and second annular strength members with respect to at least some radial vibrations at a frequency lying in the range 5 Hz to 50 Hz;
the first annular strength member is constituted by a metal ring which presents two openings disposed respectively in register with the first and second hydraulic chambers, these two openings being separated from each other by said first and second bearing zones which are constituted by stamped portions of the metal ring;
the first and second hydraulic chambers are occupied in part by inserts adapted to limit radial movements between the inner strength member and the first and second annular strength members;
the inner strength member has two bulges projecting outwards respectively into the first and second hydraulic chambers in register with the inserts disposed in said chambers;
the inner strength member presents at least one axial end secured to a rigid abutment member which extends substantially radially relative to the central axis overlying at least part of the second annular strength member, elastomer studs being interposed axially between said abutment member and a first end of the second annular strength member; and
the second axial end of the second annular strength member has elastomer studs extending axially away from said abutment member.
The invention also provides a motor vehicle comprising a body supported at least by a front axle and a rear axle, the rear axle being connected to the body via at least two antivibration sleeves as defined above, each sleeve being disposed with its central axis oriented vertically and with its first and second radial directions oriented in such a manner as to correct deformations of the rear axle tending to make said rear axle oversteer, each antivibration sleeve supporting a static vertical compression load oriented in such a manner as to urge the inner strength member in said first direction relative to the first annular strength member.